It is common practice among vehicle manufacturers to apply wax or other protective coatings to the inner cavities of vehicle body components such as doors, rear deck and hatchback lids, hoods, fender panels, frame components and underbodies. The intent is to provide a uniform, uninterrupted coating of protective material on the inside surfaces of enclosed cavities as well as along the hem flange areas of such components and other areas where water and corrosive materials are most likely to collect.
In most vehicle assembly lines, protective coatings are currently applied to body components manually by an operator using a hand-held spray gun. Prior art hand-operated spray guns generally comprise a gun body formed with a wax delivery passageway connected to a nozzle having a discharge outlet. A plunger is mounted within the wax delivery passageway which is movable between an open and closed position to control the flow of molten wax through the gun body to the nozzle. Many wax spray guns incorporate one or more atomizing air passageways which direct atomizing air into contact with a stream of molten wax ejected from the discharge outlet of the nozzle so that the wax is atomized and deposited in droplet form onto vehicle body components or other substrates.
Prior art molten wax spray guns of the type described above have a number of disadvantages. In most designs, the molten wax is recirculated outside of the spray gun when the gun is not in use, e.g., through an exterior recirculation block connected to hoses leading to and from a heated tank or other source of molten wax. The wax located within the wax delivery passageway of the spray gun remains in place when the spray gun is turned off and is allowed to cool and form a cold slug of wax within the gun. In order to resume a spraying operation, this cold slug of wax must first be pushed outwardly through the wax delivery passageway and nozzle before the warm, molten wax can flow. As a result, the spray gun is exceedingly slow to "open", i.e., a relatively long time elapses once the trigger is depressed in order for the molten wax to displace the cold slug of wax within the spray gun and then move along the entire length of the wax delivery passageway in the gun to the discharge outlet of the nozzle where it is dispensed.
Another problem with prior art wax spray guns is that atomization of the molten wax is often incomplete. A solid stream of molten wax is ejected from the discharge outlet of the nozzle in the gun body which is impacted by one or more streams of atomizing air directed at the exterior of the stream. Due to the highly viscous nature of the molten wax, the atomizing air in prior art spray guns often fails to completely convert the solid stream of molten wax to droplet form before it reaches the vehicle body component or substrate to be coated. This can result in an uneven, nonuniform coating on the target and/or gaps in the coating.
A number of vehicle body components which must be coated are of irregular shape and include a number of crevices along their inner cavities. In addition, access openings for spraying such body components are often small and/or permit limited manipulation of the hand-held wax spray gun. As a result, nozzle attachments for wax spray guns have been designed to direct the flow of molten wax to the desired areas of the vehicle body component. In many instances, these nozzle attachments have been essentially hand made and usually include cylindrical tubes which are bent or pinched at various angles to obtain the desired coverage.
One problem with nozzle attachments of this type is that the coverage of coating material on a body component which is obtained from one nozzle attachment might not be repeated with another nozzle attachment, and thus there is no assurance that a coating of proper uniformity and coverage will be obtained after each spraying operation. In addition, it is often difficult to obtain the coverage desired because of space considerations, i.e., there may not be sufficient space to provide enough spray nozzles and accompanying atomizing air jets on a nozzle attachment to ensure the entire area to be coated receives a uniform wax coating.